1. Field of the Invention
The present invention relates to an integrated optical element with a plurality of regions that differ in optical characteristic according to locations, wherein said regions each are of a structure with a two-dimensional or three-dimensional periodicity in refractive index and are combined together so that the periodicities in refractive index of said regions are different in direction from each other, and a method for making the same.
2. Description of the Related Art
Optical materials that have been used up to now are materials existing in the natural world, and they are classified into amorphous materials and crystalline materials. An amorphous material has no dependency on direction in optical characteristic. A crystalline material is anisotropic in relation between its crystal axes and the traveling direction or polarization direction of light. However, such a direction is specifically determined in a crystalline material of one kind. Therefore, in case of either amorphous materials or crystalline materials, realizing different optical characteristics in a single optical element has only been possible by combining different materials with one another by means of an adhesive agent and the like.
Since the present invention covers a very wide range of applications related to an optical element, a polarizer is taken as an example of them. Polarizers in use at present in order to obtain a specific polarization state can be classified on the basis of their action manners into (1) a polarizer to absorb unnecessary polarized waves and (2) a polarizer to separate polarized waves into separate optical paths.
A polymer film containing dichroic molecules such as iodine and the like is common as a polarizer performing the action of item (1) described above. This provides an inexpensive and large-area polarizer but has a disadvantage of being low in extinction ratio and inferior in temperature characteristic.
In order to solve this problem, a polarizer using a material that is high in stability has been developed. That is to say, this is formed by arranging an absorber such as metal, semiconductor or the like in the shape of fine lines or thin films in one direction inside a transparent body of glass or the like. A polarized wave component parallel with fine lines or thin films is absorbed or reflected and a polarized wave component perpendicular to them is transmitted.
Since a drawing process is used for any one of the above-mentioned polarizers, it is impossible to make a transmitted polarized light have the dependency on location. Therefore, in order to make it have the dependency on location, it is necessary to stick together a plurality of sheets of materials that are different in polarization direction of transmitting.
On the other hand, for a polarizer using doubly refracting crystal as a polarizer of item (2), a material large in double refractive index such as calcite and the like is used. A structure formed by sticking two triangular prisms together or a wedge-shaped structure is used, and thereby divides polarized lights into different optical paths. Since they each use a natural crystal, its crystal axes are specifically determined and it is impossible to realize crystal axes with different directions at optional locations in a single crystal. Therefore, in case of attempting to make different polarized lights pass through different regions, it is necessary to combine crystals with crystal axes of different directions.
As a polarizer using Brewster's angle of a transparent body, there is mentioned a polarization beam splitter using a dielectric multilayer film. This has a dielectric multilayer film located obliquely to the incident direction of light. Therefore, in case of attempting to make its polarization characteristic have the dependency on location, it is necessary to arrange a plurality of multilayer films in different directions, and it is apparent that this cannot be realized by means of a single element.
Another example is a wave plate. A wave plate generally in use utilizes the double refractivity of a crystallized quartz plate. Therefore, the material itself is expensive and a high-accuracy thickness control is required for making a wave plate act as a ¼-wavelength plate or a ½-wavelength plate. Further, making the optical characteristic of a single element have the dependency on location can only be realized by arranging a plurality of wave plates.
Thus, an object of the present invention is to solve the above-mentioned problems, realize a structure with an optional optical characteristic at an optional location in it and thereby realize an optical element with a high functionality not obtained from the natural world.